1. Field of the Invention
The present invention relates to a machining center and a method for manufacturing the same, and more particularly, to a machining center having a spindle head equipped with direct-drive transmission components.
2. Description of the Prior Art
According to the known technique regarding conventional multi-axis machining centers, intermediate transmission components such as a timing belt units, gear-rack units, worm-gear units, bevel gear units, spur gear units, or combinations of said units are typically implemented for operatively connecting a spindle head and a distant spindle motor which drives the spindle head. To satisfy machining requirements of complex surface structures of machine dies or aero parts, the spindle head has to be kept at a particular angle with respect to the surface being machined throughout the machining process. Once the contour variation of the surface being machined occurs, adjustment is required by spindle head to maintain the required angular relationship between the spindle head and the machined surface.
To such a conventional spindle head assembly with the presence of the intermediate transmission component as preciously discussed, the machining efficiency thereof can be significantly limited because the spindle head has to be slowed down from a preset cutting speed before being imparted with a currently required operational angle and then be sped up to the preset cutting speed to proceed with the machining work. As direct drive spindle assemblies eliminate the need of intermediate transmission components, much recent interest has been directed towards the development thereof. For instance, U.S. Pat. No. 5,584,621 has disclosed a direct drive spindle assembly comprising a pair of mutually perpendicular direct drive motor assemblies so that the spindle head is allowed to be kept at a particular angle with respect to the surface being machined despite contour variation of the machining piece. However, each the motor assembly thereof has its stator disposed outside the rotor and this causes difficult fabrication. Particular to the motor assembly with respect to axis A, all the components have to be configured and installed in sequence from the fork arms toward the center therebetween. Also, since the fork arms are cast into an integral body and possess less adjustability, it is difficult to achieve precise assembly and operation. Therefore the problems of poor control of precision and oil-leakage during operation may occur frequently. Dissimilarly, U.S. Pat. No. 6,669,416 has taught another type of direct drive spindle head characterized by the external rotor motors it implements for both the axes of rotation. Nevertheless, the included angle between the two rotational axes is 45 degree and is detrimental to the machining precision as well as the mechanical strength.
Thus, a need exists for a direct drive spindle assembly, which is advantaged by its easy assembly, alleviated oil-leakage during operation, improved mechanical strength and reduced power transmission loss.